The present invention is related to an optical pointing device and a low power image sensor used therein. In general, an optical mouse or a finger mouse senses a mouse pad or a fingerprint and computes a direction and a speed of motion, thereby accomplishing a pointing function.
A conventional optical or finger mouse includes an image signal processing chip as shown in FIG. 1.
FIG. 1 illustrates an image sensor of sensing image information such as the mouse pad or the fingerprint.
A shutter controller is a circuit for adjusting an integration time for each pixel of the image sensor in order to adjust sensitivity. An analog/digital (A/D) converter is a circuit for converting an analog signal output from the image signal into a digital signal, and generally outputs a more than 4 bit gray scale signal.
A preprocessor converts the more than 4 bit digital image signal into a 1 bit signal to make motion computation easy. Thus, the preprocessor has to have a complicated digital signal processing (DSP) function such as a discrete cosine transform (DCT) for obtaining optimum information about the 1 bit image.
A motion computing unit compares a present image with a previous image to calculate the direction and the speed of the motion. Last, a personal computer (PC) interface transmits information calculated by the motion computing unit to a PC.
To easily calculate the direction and the speed of the motion, the 1 bit image is needed and thus the preprocessor is a necessary element. However, the preprocessor having the complicated DSP function is in need of a large chip area and consumes much power. Particularly, it is required to be small in size, consume less power and process an image rapidly so as to be used in a small mobile device, but the conventional image sensor does not satisfy these requirements.
Further, to employ the optical pointing device as an input device for the small mobile device, it needs to minimize power consumed in the motion computation and to have various input functions such as a click estimation function and the like besides a motion estimation function, but there is a limit in conventional technologies.